Lift bridge



June 24, 1930. R. E. DODGE LIFT BRIDGE Filed Aug. 26, 1924' 2 sheets-sheet 1 ESEV June 24, 1930. R. E. DGDGE ,7

LIFT BRIDGE Filed Aug. 26, 1924 2 Sheets-Sheet 2 Patented June 24, 1930 new? RALPH E. nonen, or SAN FRANCISCO, oALIroRniA LIFT BRIDGE- Application filed August 26, 1924. Serial No. 734,270.

The invention relates to 'lift bridges and particularly to means for counterbalancing the weight of the bridge span.

I An object of theinvention is to provide 5 a vertically movable bridge span having counterweight leversfor counterbalancing the weight of the span, so connected to the span that the liftingeifect of the counterweights remains constant for varyingangular positions of the counterweightlevers.

A further object of the invention is to provide means connecting the counterweight levers with the span so that the force of the counterweights is applied vertically to the 1.5 span, regardless of the angular position of the levers. I j

A further object of the invention is to provide a counterbalanced bridge span with means for maintaining accurate counterbalance of the span during its vertical movement. A further object of the inventionis to provide a counterbalanced bridge span with means for moving the span vertically.

The invention possesses other advantageous features, some of which With the fore going, will be set forth at lengthin the fol: lowing description where I shall outline in full that form of the invention which I have selected for illustration in the drawings accompanying and forming part of the present specification. In said drawings. I Y have shown one form oflift bridge embodying my invention,butit is to be understood that I do not limit myselftosu'ch form since the invention, as set forth in the claims, may be embodied in a plurality of' forms.

Referring to said drawings: Figure 1 is aside elevation ofta liftl'bridge '40 constructed in accordance with myinvention. i l. I 4 Fig ure'2 is a plan view offa, section of the brid e span, showing themeans for raising and owering thespan. igureB 1s a cross section'- taken on the line Figure 2.. i v a .This invention relates to .lift bridgesin which the bridge spanis vertically movable. In order-to facilitate the lmovement of the span and to reduce the energy required to.

move the span, the span is counterbalanced so that only a small amount of power is required to move the span vertically in either direction. The spanis usually counterbalanced by counterweight levers fulcrumed on fixed supports at opposite ends of the: span, the outer ends of the levers being provided with counterweights and the inner ends of the levers being connected to the span by a simple link. Due to the fact that the levers assume .diiferent angular positions as the span moves vertically, the effective moment produced by the weight varies so that if the lever moment necessary to lift the span does notvary accordingly the effective pull of the counterweight will vary for different positions of the counterweight arm. The inner end of thelever moves in a circle as the: lever moves about its fulcrum and consequently such inner end of the lever'is displaced laterally with respect to path of .moment of the span, as the span is moved ver-. tically. If a single link is employed connecting the end of the lever with the span, the inclination of this link will vary as t he span moves vertically; causing the production of a variable horizontal component of the lifting force. I a

If the force of thecounterweight is divided between a vertical component equal to the. weight being lifted and a Tvariable horizontal component then it is clear that the counterweight will not. accurately'baL' ancethe span for all positions. In accordance with ny invention, the effective point of application of thecounter balance lever is caused to shift relative to the path of movement of the span. so that the magnitude offthe horizontalcomponent may be controlled. This horizontal componentmay be made constant so that the counterweight will always exert thesanie' lifting efifect on af'span regardless of its position. This is' accomplished byconnectin'gjthe applied end of the counterweight lever to thespani atja plurality of spaced points and then provid-; ing' a' linkage connection" which will cause the effective points of application to' shift between these two points as the applied end two of the counter lever shifts laterally with respect to the movement of the span.

The lift bridge of my invention comprises a span 2 of any suitable construction, which spans the gap between the ends of the two approaches 3. Disposed at each end of the span is, a fixed support or tower 4 and fulcrumel on each support is a counterbalancing lever 5, preferably in the form of a truss. The lever preferably extends in. the direction of the lengthof the span and each lever is provided at its outer end with a counter: weight 6 of suliicient mass to counterbalance one-half the weight of the span, so that the counterweights counterbalance the weight of the span. V

The span 2 is movable vertically and during such vertical 'movement, the levers 5 are rocked on their fulcrums 7 so that they assume varying angular positions with respect to the horizontal. The counterweight 6 is attached to the lever at a fixed pointof connection, causing the mass of the'counterweight to be effective at a fixed point, so

that as the lever 5 moves about its fulcrum,

the effective lever arm of the counterweight (Sis varied and consequently the counterweight momentcis varied, In accordance with my invention I provide means for compensating for this varying counterweight moment, so that the lifting moment applied to thespan is substantiallyequal to the counterweight moment during the angular movement of the lever 5. During the movement of the lever 5 the inner end thereof swings inan arc, so that it has relative horizontal 'movement with respect to the span. Since the span is to be moved vertically, this relative horizontal movement of the inner end of the lever 5 will tend to break the counterweight forceinto a horizontal component and a vertical component. I Since the horizontal component will vary, the result- 7 ant force necessary'to' produce a vertical the weight of the span.

\ component equal to the weight lifted will alsovary, thereby causing a variation in the lifting efiect of the counterweight, so that the counterweight will not counterbalance In accordance with my invention, I so connect theend of the lever with the span that the angular move-V ment of the leverin varying ithe effective counterweight pull, is compensated for so thatthe counterweight effect remains substantially, constant. In the present construction,- this is accoinplishedby means of r a rocking lever 12 pivoted intermediate its ends to the inner end of the lever 5.

The ends of the rocking lever 12 are connected by cross. links 13 and 14 to the span 2 at horizontally spaced points,the spacing of the -points andithe length of the rocking lever '12, determining the angularity of the links 13 andlhas the span moves vertically. The'length ofthe rocking lever 12 and the distance between the points of connection of the links 13 and 14: to the span is such that the effective point of application of the span shifts as the angularity of the counterweight lever is varied. s

The vertical distance between the fulcrum of the rocking lever .12 and a' horizontal line in the span, remains substantially constant as the counterweight lever moves about its fulcrum, indicating that any horizontal force components that may XiStTG- main substantially constant so that the counterweight is effective to produce a substantially constantvertical force. I prefer to construct the span and the counterweight levers so'that the system will operate as if the centers of mass of the system lie below the fulcrums 7. When the counterweight levers are horizontal, the centersvof mass of the span, levers and counterweights will lie vertically below the fulcruins 7 and as the angularity of the levers 5 varies, the centers of mass are simultaneously moved outward or inward below the fulcrumsT. That is, the system is adapted to be slightly off balance so that the system is therefore in the nature of a'pendulum, with itsposition of rest occurring when the levers 5 are lloil zontal. There is therefore a force tending to raise the span from its lower position and this force gradually diminishes as the span approaches itsh'alfw'ay position and from there upward the force occasioned by the off balancing of the system is in the downward direction. In raising the span this force assists in overcoming the inertia of the span during half of its movement and opposes the momentum of the span during" the last half of its movement. The same effect is produced when the span is lowered, so that the amount of energy required to 'movethe span is reduced'to a minimum. This effect also serves to reduce the wear on the brakes which are used for stopping the movement ofthe span. 1 I I Means are provided for moving the span 7 vertically and due to. the c ounterb'alancing of th'e'weight of the span, only a small amount of energy is frequiredto .rnov e the span. Secured to each support 4 midway 17 carries agear 18 which meshes with a 'rpinionlt) on the drive shaft which ei:-

t'ends longitudinally of the span from end to end and which is connected-to. a driving 7 motor "22 through "a, suitable speed redi'icing gearin 23. The pinion'lt i's held from lateral movement with respect 'to-the rack 15 bythe fi a nge dguide rollers 24 mounted I on the shaft 17, with the flangets engaging thei iij it atta k l'l s. Pijh n .6 i h ld in mesh with the rackie 1337a "tone/r25 mounted on a shaft secured to the span and bearing against the rack support 26 on the opposite side of the rack. By making the gears 18 and 19 of different widths, one gear may slide longitudinally with respect to the other, due to thermal expansion of the span, without becoming disengaged. F or this same reason the shaft 17 floats longitudinally in its bearings on the span, to permit the hearings to move longitudinally,

without causing longitudinal movement of the shaft 17 as the span expands and contracts. I

By virtue of this construction, the span is moved vertically into and out of position between the ends of the approaches 3, is substantially counterbalanced in all of its positions, and is movable vertically by the expenditure of a small amount of energy.

While I have described the present invention as embodied in a lift bridge it is to be understood that the invention is not limited to a lift bridge, but may be employed in connection with any vertically movable structure, such as, an elevator platform or floor and by the word span it is to be understood that I mean a bridge span or its equivalent, in the present instance, comprising any vertically movable structure.

I claim:

1. In a device of the class described, a span adapted to be moved thru a given path, a support adjacent said span, a pivoted counterbalance lever mounted on said support, one end of said lever extending over said span, a plurality of links connecting said end of the lever with two spaced points on the span whereby the effective point of application of the force of the lever is caused to shift between said points for different positions of the span.

2. A bridge comprising a vertically movable span,'a fixed support at each end of the span, levers fulcrumed on said supports, a rocking lever fulcrumed on each lever and links connecting each rocking leverto spaced points on the span.

3. A bridge comprising a vertically movable span, a fixed support at each end of the span, levers fulcrumed on said supports, a

rocking lever fulcrumed on each lever and cross links connecting the ends of each rocking lever with the span at spaced points.

4. A bridge comprising a vertically movable span, a fixed support at each end of the span, levers fulcrumed on fixed pivots onsaid supports, counterweights on the outer ends of said levers, a rocking lever pivoted to the inner end of each lever and cross links connecting the'ends of each rocking lever with the span at fixed points. v

In testimony whereof, I have hereunto set my hand.

RALPH E. DODGE. 

